1. Field of the Invention
The present invention relates to a method for evaluating a fixing member, more specifically, to a method for evaluating a fixing belt and/or a thermal fixing roller used in an electrophotographic apparatus or the like, and also relates to such a fixing belt and such a thermal fixing roller,
2. Description of the Prior Art
FIG. 21 is a schematic sectional drawing for explaining an image forming process in an electrophotographic apparatus. The schematic drawing represents a process of forming a monochromatic image. However, in the process of forming a full color image, developing units for four different colors, i.e., red (magenta), blue (cyan), yellow (yellow) and black (black) as well as a mechanism for mixing or superimposing the four color images are employed.
The electrophotographic apparatus (for instance, a copy machine or a laser printer) is equipped with a rotary photoconductor drum 1. A photosensitive layer on the photoconductor drum 1 is uniformly charged by an electrostatic charging unit 2, and then exposed by a laser beam 3 emitted from a laser-scanning unit. Moreover, in a developing device 4 of the electro-photographic apparatus, an electrostatic latent image, which is formed on the photoconductor drum 1, is developed by a toner, and a toner image is produced. Consequentially, the toner image is transferred to a recording paper 6 with the aid of a transfer roller 5. Furthermore, reference numeral 7 denotes a power supply unit (power pack) for applying voltage, reference numeral 8 denotes a surface electrometer for measuring a surface potential of the photoconductor drum 1, and reference numeral 9 denotes a cleaning unit for cleaning the surface of the photoconductor drum 1.
In the following, a thermal fixing apparatus used for thermally fixing the toner image transferred onto the recording paper 6 will be described. Traditionally, it is known that a roller-type thermal fixing apparatus 10, as shown at the upper left in FIG. 21, is used to thermally fix a toner for a monochromatic image (only back toner). Such a thermal fixing apparatus 10 is equipped with a thermal fixing roller 11 and a press roller 12 which are disposed in parallel to each other in order to put or sandwich a recording paper 6 between the thermal fixing roller 11 and the press roller 12. The thermal fixing roller 11 includes a hollow cylindrical core body made of aluminum or the like, and an adhesion-preventing layer for preventing toner from adhering is coated onto an outer circumferential surface of the core body, where the layer is made of fluorocarbon resin or the like. Moreover, heaters as a halogen lamp or the like (not shown) are disposed parallel to the center line of the hollow space inside the core body of the thermal fixing roller 11, thereby enabling the roller main body to be heated from the inside thereof by the radiation emitted from the heater. The movement of the recording paper 6 between the thermal fixing roller 11 and the press roller 12 causes the toner on the recording paper 6 to be softened (molten) due to the heat from the thermal fixing roller 11, so that the toner is fixed onto the recording paper 6 with the aid of the press roller 12.
The above-described thermal fixing roller having a fluorocarbon resin layer is excellent as for the toner separation ability (releaseablity), but it is inferior as for both the flexibility and elasticity, so that such a fixing roller is not be able to be suitable for using in a full color copying machine and/or a full color laser printer, which requires a glossy printing surface. Four types of color toners are conventionally used in the full color copying machine or the laser printer of the glossy image. These four color toners have to be mixed in a molten state when the color image is fixed. In other words, the four color toners are prepared to be easily molten by lowering a melting point, and several color toners must be uniformly mixed in the molten state in which the toners are wrapped on the surface of the thermal fixing roller. Therefore, it is particularly important for the surface of the thermal fixing roller to have an appropriate flexibility and elasticity. (Reference to Japanese patent laid-open Hei10-198201)
On the other hand, it is also known that a belt-type thermal fixing apparatus 15, as shown at the lower left in FIG. 21. In the thermal fixing apparatus 15, a layer-shaped fixing belt 18 is wounded between a fixing roller 16 and a heating roller 17, and further a press roller 19 is disposed in parallel to the fixing roller 16. In this arrangement, the heating roller 17 heats the fixing belt 18, and then a recording paper 6 passes through a contact surface between the fixing roller 16 and the press roller 19. The recording paper 6 is heated in the course of the passage, so that a toner image is transferred onto the recording paper 6 and then fixed thereon.
The above-mentioned fixing belt 18 has a gummy elastic layer made of silicone gum, fluorocarbon gum or the like on the surface. Such an elastic layer provides an excellent flexibility and elasticity. However, the toner separation ability is lacked, so that the toner-offset phenomenon often occurs.
In recent years, taking these facts into account, a fixing belt and a thermal fixing roller have been proposed, which are formed by coating a gummy elastic layer on a base element and further by coating a toner separation material of fluorocarbon resin or the like on the gummy elastic layer.
However, the fixing belt or the thermal fixing roller in the prior art in which such a separation layer made of a fluorocarbon resin is coated onto the gummy elastic layer, causes important properties required for the surface of the fixing belt and the thermal fixing roller, i.e., the flexibility and the elasticity, to be deteriorated.
The fixation of the toner with a fixing belt or a thermal fixing roller having inadequate flexibility and elasticity provides either a matt pattern in an image (unevenness in the image intensity). Moreover, when an image is fixed on an OHP sheet, an opaque pattern in an image on an OHP sheet is caused.
Such a problem no longer arises, if it may be ascertained with case whether or not a fixing belt or a thermal fixing roller has an appropriate flexibility and elasticity. Unfortunately, there is no conventional method for synthetically evaluating the hardness of the separation layer, taking into account the influence of the base element and the elastic layer thereon.